The components of high-temperature mechanical systems, such as, for example, gas-turbine engines, must operate in severe environments. For example, the combustor liners exposed to hot gases in commercial aeronautical engines typically experience coating surface temperatures of up to about 1150° C. to about 1400° C.
Some components of high-temperature mechanical systems include a ceramic or ceramic matrix composite (CMC)-based substrate. The substrate can be coated with an environmental barrier coating (EBC) to reduce exposure of a surface of the substrate to environmental species, such as water vapor or oxygen. The environmental barrier coating may include a ceramic topcoat, and may be bonded to the substrate by an underlying metallic or ceramic bond coat.
The component may be exposed to widely different temperatures during operation and when operation is ceased. These widely different temperatures may cause significant thermal stress to the EBC, which eventually may lead to spallation of the EBC from the substrate. The stress may be due to, for example, the substrate/bond coat and EBC having different coefficients of thermal expansion, or the substrate/bond coat and EBC experiencing different temperatures due to thermal gradients